assembly: use buffered messages in arc classifier

Beagle) grep TIMER spate-746-256x24-12.stdout
TIMER [Load input / Count input data] 3 minutes, 39.847961 seconds
TIMER [Load input / Distribute input data] 3 minutes, 50.121643 seconds
TIMER [Load input] 7 minutes, 29.969604 seconds
TIMER [Build assembly graph / Distribute vertices] 3 minutes, 41.317459 seconds
TIMER [Build assembly graph / Distribute arcs] 13 minutes, 14.808167 seconds
TIMER [Build assembly graph] 16 minutes, 56.125671 seconds
TIMER [Total] 24 minutes, 28.027832 seconds

Link: https://github.com/GeneAssembly/biosal/issues/746
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>